The overall goal of the proposed research is to understand the developmental links between perception of motor action and the acquisition of motor skill. Experience is critical for planning motor actions adaptively. Previous research shows that novice crawling and walking infants do not accurately perceive possibilities for locomotion. They attempt to cross impossibly wide gaps and steep slopes. Over weeks of locomotor experience, action participation becomes increasingly adaptive. However, long before infants acquire independent mobility, they have opportunities to observe other people perform locomotor actions. The proposed experiments examine effects of locomotor experience on action participation and action observation. Infants at 8, 12, and 16 months of age will be tested on both a participation and an observation task. In the participation task, infants will decide whether to cross possible and impossible gaps. In the observation task, they will view displays of a model infant performing the same possible and impossible locomotor actions at the edge of a gap. The research has 2 specific aims. The first aim is to examine the relationship between action participation and action observation. That is, does accurate observation of a motor action develop before, concurrent with, or after infants'ability to guide those same actions adaptively? The second aim is to examine the independent effects of age and locomotor experience on the participation and observation of motor action. Normally, age and experience are confounded. However, in the proposed research, separate effects of age and experience will be assessed with an age-matched control design to compare prelocomotor and novice crawlers at the same chronological age (8 months), and experienced crawlers and novice walkers at the same chronological age (12 months). PUBLIC HEALTH RELEVANCE: The results of the proposed studies have important implications for infants'perception of risky situations in which they are faced with the danger of falling. Falls are a common source of injury in young children, especially in infants who are just learning to crawl and to walk. A better understanding of the developmental relationship between action participation and action observation may suggest ways to decrease the frequency and severity of falling accidents.